# Explain refraction through parallel sided glass slab

In this case, we take the glass slab around a rarer medium like air. Now, if it is denser medium, the rays of light would move towards the normal. Now, the deflection of these rays due to refraction can be calculated using Snell’s law.

Snell’s law is defined as “the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given colour and for the given pair of media”.